In general, a magnetic recording medium includes a sector identification code for distinguishing one sector from another. In addition, unrecorded portions are provided between respective sectors to separate one sector from the next. It should be noted that, since noise can be generated in these unrecorded portions of the magnetic recording medium, an appropriate sync signal may not be generated at the exact starting point of a sector. That is, the noise generated in the unrecorded portion may be mistaken for the starting point of a sector, by the playback circuit, and, as a result the sync signal may be generated in the unrecorded portion.
FIG. 1A represents the conventional data recording format of a hard disk.
In FIG. 1A, a post-amble portion exists from an end location ENDS to of a sector a starting point of an unrecorded portion DC-GAP, sequentially followed by an unrecorded portion, a pre-amble portion and a data portion of the next sector.
FIG. 1B shows the location where a normal sync signal should be generated when ready a conventional hard disk. As be seen from the figure, the normal sync signal is generated at a predetermined point of the pre-amble portion.
FIG. 2 shows the location where a sync signal is generated in reading a conventional hard disk when one or two noise pulses included in the unrecorded portion are mistaken for a data signal. Thus a conventional unrecorded portion detecting circuit of the recording medium erroneously generates a sync signal by recognizing as data pulses the noise pulses in the unrecorded portion of the recording medium.